The present invention relates to paper machines in general, and more particularly to improvements in apparatus for shifting or moving suction heads, rolls, drums, cylinders and/or analogous components of a paper machine between several positions. More particularly, the invention relates to improvements in apparatus which can be used with advantage to move a suction head or a pick-up roll in a paper machine.
It is already known to mount a suction head or a pick-up roll in a paper machine in such a way that the suction head or the pick-up roll (either of these parts will be referred to as a movable component for the sake of brevity) can be moved between an operative position, an intermediate position not far away from the operative position, and a retracted position at a considerable distance from the operative position. For example, it is customary to maintain a suction head in engagement with the inner side of a foraminous felt to attract the paper web to the outer side of the felt at the locus where the web is to be separated from the wire in order to enter the press. In the event of malfunction, e.g., when the web breaks, the suction head is pivoted or otherwise moved from the operative position to an intermediate position and is simultaneously disconnected from the suction generating means so that the web continues to adhere to the wire and is caused to enter a collecting vat or an analogous receptacle for waste paper. The distance between the operative and intermediate positions of the suction head is relatively small, i.e., it does not suffice to facilitate convenient access to a wire or felt which must be removed for the purpose of inspection or replacement. Therefore, the suction head is also movable to a retracted position at a much greater distance from the operation position; this renders it possible to replace the wire and/or the felt without any or with minimal interference on the part of the suction head. The situation is the same or analogous if the component to be moved between operative, intermediate and retracted positions is a pick-up roll.
In presently known paper machines, the component to be moved between the just mentioned three positions is coupled to an electromechanical shifting or displacing apparatus, e.g., to an apparatus including a motor, transmission means, a feed screw, a servomotor and one or more limit switches. A drawback of such apparatus is their complexity; furthermore, many heretofore known apparatus employ a transverse shaft which extends between the front and rear sides of the paper machine and interferes with access to the parts which are to be reached when the movable component is held in the retracted position. Also, the presently known apparatus do not insure satisfactory engagement between the movable component and the adjacent part or parts, e.g., the felt or the paper web, because the axis of the movable component is often tilted with respect to the path of movement of the felt, wire or web. This can cause the web, wire and/or felt to run askew.